Non-native Minnows Threaten Quillwort Populations in High Mountain Shallow Lakes

Abstract

Submersed aquatic plants are a key component of shallow, clear water lakes contributing to primary production and water quality. High mountain lakes are naturally fishless although invasive trout and most recently minnows have been introduced causing a major impact on fauna richness. The Pyrenean high mountain range has preserved soft-water oligotrophic boreal isoetids in their southern limit of distribution but the recent fish introduction is a potential factor of stress that needs to be addressed. We here work under the hypothesis that due to contrasting ecological features, trout will not be heavily affecting quillwort populations while minnows will have a stronger effect on zooplankton and zoobenthos that will promote algal growth and reduce light availability for the underwater meadows. Ten Pyrenean shallow lakes representative of three scenarios -fishless, with trout and with minnows-, were sampled for meadow structure, water column and benthic environment characterization in mid-summer 2015 and 2016. Quillwort biomass allocation (above vs. belowground), epiphytic load, and composition of the algal community (abundant cyanobacteria) differed in the presence of minnows. In trout lakes biomass allocation and epiphytic load were average and the algal community composed by chlorophytes and diatoms as in fishless lakes. Biomass ratio was close to thresholds of negative buoyancy in minnow lakes indicating that meadows were at risk of uprooting and consequent de-vegetation. Total and soluble carbohydrates were lower and the sporangia contained significantly less reserves to constrain growth and expansion in the presence of minnows. Lake scenarios were coupled to physicochemical differences with low light, high phosphorus and Chl-a (mesotrophia) in minnow lakes, while trout and fishless lakes remained oligotrophic. This is the first study assessing the impact of non-native fish on soft-water isoetids from mountain lakes and shows that minnows are a major threat to quillworts. The impaired light environment (from epiphytic algal overgrow and water column Chl-a) entails consequent regression (i.e., no recruitment) and de-vegetation (uprooting) of the meadows. Since soft-water oligotrophic mountain lakes are protected under the Habitats Directive, some action needs to be urgently implemented not only to preserve quillworts but to the overall ecological integrity of the lakes.

Response of the aquatic invertebrate community to the eradication of an exotic invasive fish 30 years after its introduction into an Iberian alpine lake

“…Decreases in larger-sized zooplankton and benthic invertebrates after fish introductions were observed in North American lakes, specifically in California (Bradford et al 1998;Knapp et al 2001), Colorado (Lafrancois et al 2003), Utah (Carlisle and Hawkins 1998) and Western Canada (Donald et al 2001;Leavitt et al 1994, Parker et al 2001Schindler et al 2001), as well as in Northern Italy (Magnea et al 2013;Tiberti et al 2014), France (Cavalli et al 2001), Austria (Schabetsberger et al 2009), Portugal (Boavida and Gliwicz 1996), and Poland (Gliwicz 1980;Sienkiewicz and Gąsiorowski 2016) in Europe. Negative effects of fish introduction in lakes have also been recorded for amphibians (Braña et al 1996), submerged macrophytes (Gacia et al 2018) and natural fish assemblages (Miró and Ventura 2015) in Spain: these introductions also resulted in increases in the abundance of patogens and virulent bacteria in Northern Italian lakes (Pastorino et al 2018). However, no significant differences were found for large zooplankton species densities or for the composition of the zooplankton assemblages in a few cases when comparing lakes with and without fish, as in Switzerland (Winder et al 2001) and Bolivia (Aguilera et al 2006).…”

“…During the last century, in order to expand the possibilities of sport fishing in mountain areas, some non-native fish species were released for angling in many Iberian high mountain lakes. Most of them were salmonid species, well adapted to these cold environments: (Gacia et al 2018;García-Berthou et al 2015;Miró and Ventura 2015;Toro et al 2006;Ventura et al 2017).…”